The present invention relates to a novel process for the crystallization of xylitol, to a particulate crystalline xylitol product having novel properties, to the use thereof in confectionery, foodstuffs, pharmaceuticals and oral hygiene products, and to special products comprising the same. The present invention specifically provides a crystalline xylitol product, wherein the crystals are produced by microcrystallization of xylitol from a liquid solution of xylitol.
Xylitol is a naturally occurring five carbon sugar alcohol which has the same sweetness as sugar and a caloric content which is less than that of sugar. Xylitol is found in small amounts in many fruits and vegetables and is produced in the human body during normal metabolism. Xylitol is attractive as a sugar substitute in food contexts because of its known metabolic, dental and technical characteristics. Xylitol is metabolized largely independent of insulin, so it can be safely consumed by non-insulin dependent diabetics.
Xylitol is well established as a non-cariogenic substance, i.e. xylitol does not contribute to caries formation. Significant data also exists which supports the view that xylitol is not only non-cariogenic, but actively suppresses the formation of new caries and may even re-harder existing lesions by inducing remineralization, i.e. it is a cariostatic material.
A summary of clinical data regarding the effects of xylitol and its possible mechanisms is set forth in Bar, Albert, Caries Prevention With Xylitol: A Review of a Scientific Evidence, 55 Wld. Rev. Nutr. Diet. 183-209 (1983); Tanzer, Jason M., Xylitol chewing gum and dental caries. International Dental Journal (IDJ), Vol. 45, No. 1. (Suppl. 1), 65-76 (1995); Edgar, W. M., Sugar substitutes, chewing gum and dental cariesxe2x80x94a review. British Dental Journal (BDJ), Vol. 184, No. 1, 29-32 (January 1998).
Xylitol has been widely used as a sweetening agent resembling sugar. For instance, xylitol may be used in confectionery, bakery products, cereals, desserts, jams, beverages, chocolate, chewing gums, ice-cream, and in various dietetic products. Xylitol has also been used in the production of oral hygiene products such as tooth pastes, and in the manufacture of pharmaceuticals.
Xylitol has been commercially produced in crystalline form, the crystallization being performed by conventional liquid crystallization techniques from an aqueous solution. The properties and production of xylitol has been described, for instance, in Carson, J. F. et al, J. Am. Chem. Soc. 65 (1993) p. 1777-1778; Kim, H. S. et al, Acta. Cryst. (1969), B25, 2607; Nabors, L. O. et al. Alternative Sweeteners, Second Ed., 1991, p. 349-352; as well as U.S. Pat. No. 4,066,711 and 4,698,101.
The crystallization of xylitol from a liquid such as from an aqueous or ethanolic solution requires specific crystallization conditions and fairly long crystallization times due to the nature of prior art crystallization methods, all of the xylitol in the solution cannot be obtained in crystalline form. A part of the xylitol will always remain in the mother liquor and will be discarded with the mother liquor even after repeated series of crystallizations. This provides a comparatively low yield of the process.
Xylitol has also been produced in solid form by granulation as described in U.S. Pat. No. 5,204,115. Granulation of xylitol with a binder such as polydextrose has been shown to improve the tabletting properties of xylitol. There is no disclosure of successful spray drying of xylitol alone.
In connection with spray drying of sorbitol, minor amounts of xylitol or other polyols have been added to the spray solution As described in DE Patent 44 39 858 (Merck Patent GmbH). According to the said Patent, 5% or 7.5% of xylitol, respectively, were added into an aqueous sorbitol solution and spray dried to provide a tablettable product. There is no indication that xylitol alone has been spray dried in the same manner.
Thus, there exists a need for improving the production of solid xylitol products and the present invention aims at satisfying that need.
The object of the present invention is thus, to provide a solid particulate crystalline xylitol product.
Another object of the present invention is to provide crystalline xylitol product in a process which transforms a xylitol liquid into a solid xylitol product in one single overall operation.
An object of the invention is also to provide a novel particulate xylitol product which is suitable for use in the food industry as well as in the pharmaceutical and oral hygiene product industry.
An object is also to provide novel edible, pharmaceutical and oral hygiene products containing xylitol.
Consequently, the present invention, which is defined in the appended claims, provides a novel process for producing crystalline xylitol. Said process comprises contacting a liquid containing dissolved xylitol with gas suspended solid particles containing microcrystalline xylitol; causing substantial removal of the solvent component of said liquid and allowing the resulting xylitol material to form an essentially solid composition of matter comprising a multitude of microcrystals of xylitol; and causing said xylitol composition to be conditioned during a further drying step to provide a product consisting essentially throughout its entire structure of a multitude of microcrystals of xylitol agglomerated together in a random manner.
In a preferred embodiment of the invention an aqueous solution of xylitol is brought into contact with fluidized particles of microcrystalline xylitol, the wetted particles are dried in a flow of hot gas, and the xylitol on the surface of the particles is allowed to form new microcrystals on said surface.
By further conditioning the particles, the microcrystallization is allowed to proceed for a sufficient time to provide a final product consisting essentially of microcrystalline xylitol.
In a preferred embodiment of the invention the wetted particles are substantially dried while falling down with a co-current air stream and allowed to settle into a porous layer of agglomerated microcrystallizing xylitol, which is then conditioned and cooled. The microcrystallization conditions are selected so that the cooled layer is dry, porous and brittle. If desired, the layer may be broken up into smaller fractions. Only a mild crushing action is needed to break up the agglomerated mass of microcrystals. The agglomerated product will primarily be broken up at the interfaces between individual crystals rather than by disrupting the crystals themselves.
In another embodiment of the invention the particles are retained in a suspended state in an air stream while additional liquid is sprayed onto their surfaces until the particles have grown to a predetermined size or weight. The particles are then removed from the air stream, e.g. by gravity and conditioned as described above.
The gas suspended microcrystalline xylitol particles are preferably provided by recirculating a portion of the microcrystalline xylitol produced in the process itself. Said particles may comprise dust entrained in circulating drying air or it may be dust or fine particles provided by the crushing of the agglomerated microcrystalline mass. In the absence of microcrystalline xylitol, the solid feed of the process may at start-up comprise milled crystalline xylitol from another source. This solid feed should, however, be progressively replaced by microcrystalline xylitol in order to provide a totally microcrystalline structure to the product.
The terms xe2x80x9cmicrocrystallinexe2x80x9d and xe2x80x9cmicrocrystalxe2x80x9d as used throughout the present specification and claims should be understood to mean very small crystals having a size which on an average is below 50xcexc, and generally is of the order of about 10xcexc, on an average. In contrast to the present microcrystals, the xylitol crystals obtainable by prior known crystallization techniques are discrete crystals the particle size of which, on an average, is of the order of about 100-1000xcexc or larger.
Consequently, the present invention provides a novel particulate crystalline xylitol product wherein each particle substantially throughout its entire structure consists of a multitude of microcrystals of xylitol agglomerated together in a random manner.
Although the size of the xylitol particles according to the present invention is not critical and may vary according to the intended use of the product, the mean particle size of the xylitol product is generally between about 0.1 and 1.0 mm. The preferred mean particle size is generally about 0.15-0.4 mm. The particle size and distribution may be controlled to suit the intended use.
The microcrystals may be used as such from the process, they may be broken up or they may even be cast in the form of ordinary sugar lumps or cubes.
The individual xylitol microcrystals generally comprise anhydrous xylitol. The crystal mass may also include minor portions of amorphous xylitol. In a preferred embodiment of the invention, the microcrystals consist essentially of anhydrous xylitol.
The microcrystalline xylitol product according to the present invention may be used as a bulk sweetener for the total or partial replacement of sucrose or other sweetening agents. Thus, it is useful in dietetic products, in confectionery, bakery products, cereals, desserts, jams, beverages, especially in chocolate, granulated or tabletted table top sweeteners, chewing gums and ice creams, etc. It is also useful in pharmaceuticals where it may comprise the active ingredient or may be included as sweetener, an excipient, a diluent and/or a carrier. The present microcrystalline xylitol may also be used in the production of personal care products and oral hygiene products such as tooth pastes, mouth rinses, etc. The microcrystalline xylitol product according to the present invention can be tabletted into a hard tablet.
A further embodiment of the present invention, relates to a special sweetener which comprises microcrystalline xylitol. Such a sweetener may include other components such as excipients and/or other sweeteners.
Such other sweeteners are preferably also non-cariogenic sweeteners such as intense sweeteners taken from the group comprising dipeptide sweeteners, saccharin, acesulfame K, stevioside, cyclamate, sucralose and neohesperidin dihydrochalcone. However, the preferred non-cariogenic sweetener consists essentially of the microcrystalline xylitol according to the invention.
The other components which may be used in the sweetener and/or other applications such as in pharmaceutical preparations may comprise, for instance, microcrystalline cellulose, carboxymethyl cellulose, polydextrose, dextrose, maltodextrin, lactose, sugar, etc. as well as other sugar alcohols.
The microcrystalline xylitol of the present invention is preferably produced in a pure xylitol form, i.e. containing throughout essentially only xylitol. Thus, the present solid xylitol product can be produced totally without separate binder, which is contrary to the product granulated according to U.S. Pat. No. 5,204,115 with a binder.
The present microcrystalline xylitol may, however, also be microcrystallized with other compounds. Thus, if the solid and/or liquid feed comprises other components, such as one or more of the above mentioned excipients, or other active ingredients, the product discharged from the microcrystallization apparatus will contain said other component(s). A secondary spray of another solid or liquid component may also be fed into the nicrocrystallization apparatus into contact with the microcrystallizing xylitol.
Only such additional components can be used which do not significantly and adversely interfere with the microcrystallization according to the present invention. Specifically, it is necessary that the additional components and the amounts thereof are selected so that the microcrystallizing particles will be substantially dry by the time they leave the suspended state. If the initially dried particles contain too much moisture, they will be clogged together forming large compact structures, wherein the microcrystallization throughout the product cannot be ensured.
Further embodiments of the present invention relate to products made from the novel microcrystalline xylitol. Such products are typically edible products, pharmaceutical products and/or oral hygiene products such as those mentioned above. The microcrystalline xylitol of the present invention may, for instance, be advantageously used in the production of chewing gum. It also provides improvements in tabletting compared to conventional crystalline xylitol.
The present invention will now be described in greater detail. This description should, however, not be taken as limiting the invention to the precise wording thereof. A person skilled in the art will be able to provide numerous modifications and variations of the process without deviating from the invention as defined in the appended claims.